double ReferenceIntegrateRPMDStepKernel::computeKineticEnergy(ContextImpl& context, const RPMDIntegrator& integrator) {
const System& system = context.getSystem();
int numParticles = system.getNumParticles();
vector<RealVec>& velData = extractVelocities(context);
double energy = 0.0;
for (int i = 0; i < numParticles; ++i) {
double mass = system.getParticleMass(i);
if (mass > 0) {
RealVec v = velData[i];
energy += mass*(v.dot(v));
}
}
return 0.5*energy;
}
void ReferenceIntegrateDrudeSCFStepKernel::minimize(ContextImpl& context, double tolerance) {
// Record the initial positions and determine a normalization constant for scaling the tolerance.
vector<RealVec>& pos = extractPositions(context);
int numDrudeParticles = drudeParticles.size();
double norm = 0.0;
for (int i = 0; i < numDrudeParticles; i++) {
RealVec p = pos[drudeParticles[i]];
minimizerPos[3*i] = p[0];
minimizerPos[3*i+1] = p[1];
minimizerPos[3*i+2] = p[2];
norm += p.dot(p);
}
norm /= numDrudeParticles;
norm = (norm < 1 ? 1 : sqrt(norm));
minimizerParams.epsilon = tolerance/norm;
// Perform the minimization.
lbfgsfloatval_t fx;
MinimizerData data(context, drudeParticles);
lbfgs(numDrudeParticles*3, minimizerPos, &fx, evaluate, NULL, &data, &minimizerParams);
}
double CpuCalcNonbondedForceKernel::execute(ContextImpl& context, bool includeForces, bool includeEnergy, bool includeDirect, bool includeReciprocal) {
if (!hasInitializedPme) {
hasInitializedPme = true;
useOptimizedPme = false;
if (nonbondedMethod == PME) {
// If available, use the optimized PME implementation.
try {
optimizedPme = getPlatform().createKernel(CalcPmeReciprocalForceKernel::Name(), context);
optimizedPme.getAs<CalcPmeReciprocalForceKernel>().initialize(gridSize[0], gridSize[1], gridSize[2], numParticles, ewaldAlpha);
useOptimizedPme = true;
}
catch (OpenMMException& ex) {
// The CPU PME plugin isn't available.
}
}
}
AlignedArray<float>& posq = data.posq;
vector<RealVec>& posData = extractPositions(context);
vector<RealVec>& forceData = extractForces(context);
RealVec boxSize = extractBoxSize(context);
float floatBoxSize[3] = {(float) boxSize[0], (float) boxSize[1], (float) boxSize[2]};
double energy = (includeReciprocal ? ewaldSelfEnergy : 0.0);
bool ewald = (nonbondedMethod == Ewald);
bool pme = (nonbondedMethod == PME);
if (nonbondedMethod != NoCutoff) {
// Determine whether we need to recompute the neighbor list.
double padding = 0.15*nonbondedCutoff;
bool needRecompute = false;
double closeCutoff2 = 0.25*padding*padding;
double farCutoff2 = 0.5*padding*padding;
int maxNumMoved = numParticles/10;
vector<int> moved;
for (int i = 0; i < numParticles; i++) {
RealVec delta = posData[i]-lastPositions[i];
double dist2 = delta.dot(delta);
if (dist2 > closeCutoff2) {
moved.push_back(i);
if (dist2 > farCutoff2 || moved.size() > maxNumMoved) {
needRecompute = true;
break;
}
}
}
if (!needRecompute && moved.size() > 0) {
// Some particles have moved further than half the padding distance. Look for pairs
// that are missing from the neighbor list.
int numMoved = moved.size();
double cutoff2 = nonbondedCutoff*nonbondedCutoff;
double paddedCutoff2 = (nonbondedCutoff+padding)*(nonbondedCutoff+padding);
for (int i = 1; i < numMoved && !needRecompute; i++)
for (int j = 0; j < i; j++) {
RealVec delta = posData[moved[i]]-posData[moved[j]];
if (delta.dot(delta) < cutoff2) {
// These particles should interact. See if they are in the neighbor list.
RealVec oldDelta = lastPositions[moved[i]]-lastPositions[moved[j]];
if (oldDelta.dot(oldDelta) > paddedCutoff2) {
needRecompute = true;
break;
}
}
}
}
if (needRecompute) {
neighborList->computeNeighborList(numParticles, posq, exclusions, floatBoxSize, data.isPeriodic, nonbondedCutoff+padding, data.threads);
lastPositions = posData;
}
nonbonded->setUseCutoff(nonbondedCutoff, *neighborList, rfDielectric);
}
if (data.isPeriodic) {
double minAllowedSize = 1.999999*nonbondedCutoff;
if (boxSize[0] < minAllowedSize || boxSize[1] < minAllowedSize || boxSize[2] < minAllowedSize)
throw OpenMMException("The periodic box size has decreased to less than twice the nonbonded cutoff.");
nonbonded->setPeriodic(floatBoxSize);
}
if (ewald)
nonbonded->setUseEwald(ewaldAlpha, kmax[0], kmax[1], kmax[2]);
if (pme)
nonbonded->setUsePME(ewaldAlpha, gridSize);
if (useSwitchingFunction)
nonbonded->setUseSwitchingFunction(switchingDistance);
double nonbondedEnergy = 0;
if (includeDirect)
nonbonded->calculateDirectIxn(numParticles, &posq[0], posData, particleParams, exclusions, data.threadForce, includeEnergy ? &nonbondedEnergy : NULL, data.threads);
if (includeReciprocal) {
if (useOptimizedPme) {
PmeIO io(&posq[0], &data.threadForce[0][0], numParticles);
Vec3 periodicBoxSize(boxSize[0], boxSize[1], boxSize[2]);
optimizedPme.getAs<CalcPmeReciprocalForceKernel>().beginComputation(io, periodicBoxSize, includeEnergy);
nonbondedEnergy += optimizedPme.getAs<CalcPmeReciprocalForceKernel>().finishComputation(io);
}
else
nonbonded->calculateReciprocalIxn(numParticles, &posq[0], posData, particleParams, exclusions, forceData, includeEnergy ? &nonbondedEnergy : NULL);
}
energy += nonbondedEnergy;
if (includeDirect) {
ReferenceBondForce refBondForce;
ReferenceLJCoulomb14 nonbonded14;
refBondForce.calculateForce(num14, bonded14IndexArray, posData, bonded14ParamArray, forceData, includeEnergy ? &energy : NULL, nonbonded14);
if (data.isPeriodic)
energy += dispersionCoefficient/(boxSize[0]*boxSize[1]*boxSize[2]);
}
return energy;
}
double ReferenceCalcDrudeForceKernel::execute(ContextImpl& context, bool includeForces, bool includeEnergy) {
vector<RealVec>& pos = extractPositions(context);
vector<RealVec>& force = extractForces(context);
int numParticles = particle.size();
double energy = 0;
// Compute the interactions from the harmonic springs.
for (int i = 0; i < numParticles; i++) {
int p = particle[i];
int p1 = particle1[i];
int p2 = particle2[i];
int p3 = particle3[i];
int p4 = particle4[i];
RealOpenMM a1 = (p2 == -1 ? 1 : aniso12[i]);
RealOpenMM a2 = (p3 == -1 || p4 == -1 ? 1 : aniso34[i]);
RealOpenMM a3 = 3-a1-a2;
RealOpenMM k3 = charge[i]*charge[i]/(polarizability[i]*a3);
RealOpenMM k1 = charge[i]*charge[i]/(polarizability[i]*a1) - k3;
RealOpenMM k2 = charge[i]*charge[i]/(polarizability[i]*a2) - k3;
// Compute the isotropic force.
RealVec delta = pos[p]-pos[p1];
RealOpenMM r2 = delta.dot(delta);
energy += 0.5*k3*r2;
force[p] -= delta*k3;
force[p1] += delta*k3;
// Compute the first anisotropic force.
if (p2 != -1) {
RealVec dir = pos[p1]-pos[p2];
RealOpenMM invDist = 1.0/sqrt(dir.dot(dir));
dir *= invDist;
RealOpenMM rprime = dir.dot(delta);
energy += 0.5*k1*rprime*rprime;
RealVec f1 = dir*(k1*rprime);
RealVec f2 = (delta-dir*rprime)*(k1*rprime*invDist);
force[p] -= f1;
force[p1] += f1-f2;
force[p2] += f2;
}
// Compute the second anisotropic force.
if (p3 != -1 && p4 != -1) {
RealVec dir = pos[p3]-pos[p4];
RealOpenMM invDist = 1.0/sqrt(dir.dot(dir));
dir *= invDist;
RealOpenMM rprime = dir.dot(delta);
energy += 0.5*k2*rprime*rprime;
RealVec f1 = dir*(k2*rprime);
RealVec f2 = (delta-dir*rprime)*(k2*rprime*invDist);
force[p] -= f1;
force[p1] += f1;
force[p3] -= f2;
force[p4] += f2;
}
}
// Compute the screened interaction between bonded dipoles.
int numPairs = pair1.size();
for (int i = 0; i < numPairs; i++) {
int dipole1 = pair1[i];
int dipole2 = pair2[i];
int dipole1Particles[] = {particle[dipole1], particle1[dipole1]};
int dipole2Particles[] = {particle[dipole2], particle1[dipole2]};
for (int j = 0; j < 2; j++)
for (int k = 0; k < 2; k++) {
int p1 = dipole1Particles[j];
int p2 = dipole2Particles[k];
RealOpenMM chargeProduct = charge[dipole1]*charge[dipole2]*(j == k ? 1 : -1);
RealVec delta = pos[p1]-pos[p2];
RealOpenMM r = sqrt(delta.dot(delta));
RealOpenMM u = r*pairThole[i]/pow(polarizability[dipole1]*polarizability[dipole2], 1.0/6.0);
RealOpenMM screening = 1.0 - (1.0+0.5*u)*exp(-u);
energy += ONE_4PI_EPS0*chargeProduct*screening/r;
RealVec f = delta*(ONE_4PI_EPS0*chargeProduct*screening/(r*r*r));
force[p1] += f;
force[p2] -= f;
}
}
return energy;
}
void ReferenceIntegrateDrudeLangevinStepKernel::execute(ContextImpl& context, const DrudeLangevinIntegrator& integrator) {
vector<RealVec>& pos = extractPositions(context);
vector<RealVec>& vel = extractVelocities(context);
vector<RealVec>& force = extractForces(context);
// Update velocities of ordinary particles.
const RealOpenMM vscale = exp(-integrator.getStepSize()*integrator.getFriction());
const RealOpenMM fscale = (1-vscale)/integrator.getFriction();
const RealOpenMM kT = BOLTZ*integrator.getTemperature();
const RealOpenMM noisescale = sqrt(2*kT*integrator.getFriction())*sqrt(0.5*(1-vscale*vscale)/integrator.getFriction());
for (int i = 0; i < (int) normalParticles.size(); i++) {
int index = normalParticles[i];
RealOpenMM invMass = particleInvMass[index];
if (invMass != 0.0) {
RealOpenMM sqrtInvMass = sqrt(invMass);
for (int j = 0; j < 3; j++)
vel[index][j] = vscale*vel[index][j] + fscale*invMass*force[index][j] + noisescale*sqrtInvMass*SimTKOpenMMUtilities::getNormallyDistributedRandomNumber();
}
}
// Update velocities of Drude particle pairs.
const RealOpenMM vscaleDrude = exp(-integrator.getStepSize()*integrator.getDrudeFriction());
const RealOpenMM fscaleDrude = (1-vscaleDrude)/integrator.getDrudeFriction();
const RealOpenMM kTDrude = BOLTZ*integrator.getDrudeTemperature();
const RealOpenMM noisescaleDrude = sqrt(2*kTDrude*integrator.getDrudeFriction())*sqrt(0.5*(1-vscaleDrude*vscaleDrude)/integrator.getDrudeFriction());
for (int i = 0; i < (int) pairParticles.size(); i++) {
int p1 = pairParticles[i].first;
int p2 = pairParticles[i].second;
RealOpenMM mass1fract = pairInvTotalMass[i]/particleInvMass[p1];
RealOpenMM mass2fract = pairInvTotalMass[i]/particleInvMass[p2];
RealOpenMM sqrtInvTotalMass = sqrt(pairInvTotalMass[i]);
RealOpenMM sqrtInvReducedMass = sqrt(pairInvReducedMass[i]);
RealVec cmVel = vel[p1]*mass1fract+vel[p2]*mass2fract;
RealVec relVel = vel[p2]-vel[p1];
RealVec cmForce = force[p1]+force[p2];
RealVec relForce = force[p2]*mass1fract - force[p1]*mass2fract;
for (int j = 0; j < 3; j++) {
cmVel[j] = vscale*cmVel[j] + fscale*pairInvTotalMass[i]*cmForce[j] + noisescale*sqrtInvTotalMass*SimTKOpenMMUtilities::getNormallyDistributedRandomNumber();
relVel[j] = vscaleDrude*relVel[j] + fscaleDrude*pairInvReducedMass[i]*relForce[j] + noisescaleDrude*sqrtInvReducedMass*SimTKOpenMMUtilities::getNormallyDistributedRandomNumber();
}
vel[p1] = cmVel-relVel*mass2fract;
vel[p2] = cmVel+relVel*mass1fract;
}
// Update the particle positions.
int numParticles = particleInvMass.size();
vector<RealVec> xPrime(numParticles);
RealOpenMM dt = integrator.getStepSize();
for (int i = 0; i < numParticles; i++)
if (particleInvMass[i] != 0.0)
xPrime[i] = pos[i]+vel[i]*dt;
// Apply constraints.
extractConstraints(context).apply(pos, xPrime, particleInvMass, integrator.getConstraintTolerance());
// Record the constrained positions and velocities.
RealOpenMM dtInv = 1.0/dt;
for (int i = 0; i < numParticles; i++) {
if (particleInvMass[i] != 0.0) {
vel[i] = (xPrime[i]-pos[i])*dtInv;
pos[i] = xPrime[i];
}
}
// Apply hard wall constraints.
const RealOpenMM maxDrudeDistance = integrator.getMaxDrudeDistance();
if (maxDrudeDistance > 0) {
const RealOpenMM hardwallscaleDrude = sqrt(kTDrude);
for (int i = 0; i < (int) pairParticles.size(); i++) {
int p1 = pairParticles[i].first;
int p2 = pairParticles[i].second;
RealVec delta = pos[p1]-pos[p2];
RealOpenMM r = sqrt(delta.dot(delta));
RealOpenMM rInv = 1/r;
if (rInv*maxDrudeDistance < 1.0) {
// The constraint has been violated, so make the inter-particle distance "bounce"
// off the hard wall.
if (rInv*maxDrudeDistance < 0.5)
throw OpenMMException("Drude particle moved too far beyond hard wall constraint");
RealVec bondDir = delta*rInv;
RealVec vel1 = vel[p1];
RealVec vel2 = vel[p2];
RealOpenMM mass1 = particleMass[p1];
RealOpenMM mass2 = particleMass[p2];
RealOpenMM deltaR = r-maxDrudeDistance;
RealOpenMM deltaT = dt;
RealOpenMM dotvr1 = vel1.dot(bondDir);
RealVec vb1 = bondDir*dotvr1;
RealVec vp1 = vel1-vb1;
if (mass2 == 0) {
// The parent particle is massless, so move only the Drude particle.
if (dotvr1 != 0.0)
deltaT = deltaR/abs(dotvr1);
if (deltaT > dt)
deltaT = dt;
dotvr1 = -dotvr1*hardwallscaleDrude/(abs(dotvr1)*sqrt(mass1));
RealOpenMM dr = -deltaR + deltaT*dotvr1;
pos[p1] += bondDir*dr;
vel[p1] = vp1 + bondDir*dotvr1;
}
else {
// Move both particles.
RealOpenMM invTotalMass = pairInvTotalMass[i];
RealOpenMM dotvr2 = vel2.dot(bondDir);
RealVec vb2 = bondDir*dotvr2;
RealVec vp2 = vel2-vb2;
RealOpenMM vbCMass = (mass1*dotvr1 + mass2*dotvr2)*invTotalMass;
dotvr1 -= vbCMass;
dotvr2 -= vbCMass;
if (dotvr1 != dotvr2)
deltaT = deltaR/abs(dotvr1-dotvr2);
if (deltaT > dt)
deltaT = dt;
RealOpenMM vBond = hardwallscaleDrude/sqrt(mass1);
dotvr1 = -dotvr1*vBond*mass2*invTotalMass/abs(dotvr1);
dotvr2 = -dotvr2*vBond*mass1*invTotalMass/abs(dotvr2);
RealOpenMM dr1 = -deltaR*mass2*invTotalMass + deltaT*dotvr1;
RealOpenMM dr2 = deltaR*mass1*invTotalMass + deltaT*dotvr2;
dotvr1 += vbCMass;
dotvr2 += vbCMass;
pos[p1] += bondDir*dr1;
pos[p2] += bondDir*dr2;
vel[p1] = vp1 + bondDir*dotvr1;
vel[p2] = vp2 + bondDir*dotvr2;
}
}
}
}
ReferenceVirtualSites::computePositions(context.getSystem(), pos);
data.time += integrator.getStepSize();
data.stepCount++;
}